Rechargeable lithium ion batteries are increasingly used for a variety of energy storage applications, including for example, electric and hybrid automotive applications throughout the world. In automotive applications, particularly for all-electric vehicles, battery weight is a major hurdle for achieving longer driving range-per charge. While, lithium ion (Li-ion) batteries remain a very important commercial and research focus, there is an increasing need for new battery technologies to provide higher energy densities than are available for Li-ion.
One promising approach to higher-energy density alternative to Li-ion batteries is a battery based on a multivalent ion electrolyte, such as magnesium (Mg) or calcium (Ca). Li-ion, with a charge of +1, can provide only a single electron for an electrical current, whereas multivalent ions (e.g., with a charge of +2 or +3) have the potential to provide two or more the electrical current of Li-ions (depending on the charge of the multivalent ion) if present with the same density. Mg-ion and Ca-ion batteries have promise, however, there are also a number of issues that still need to be worked out and better understood. Calcium ion and magnesium ion provide relatively high potentials (Ca2+: −2.87 relative to standard hydrogen electrode, SHE; Mg2+: −2.37 vs. SHE) suitable for many secondary battery requirements. One of the most relevant aspects is understanding the mechanism of reversible plating and stripping of Mg at the metal anode/electrolyte interface during battery operation. So far, reversible Mg plating has been achieved with only a narrow class of electrolytes, inorganic or organic magnesium aluminum chloride salts dissolved in ethereal solutions. For example, the Mg analogues to the most common commercial Li-ion electrolytes instantaneously decompose and passivate the Mg metal anode surface preventing further electrochemical reaction, consequently blocking the battery.
There are ongoing needs for new electrolyte salts for multivalent ion batteries, particularly Mg-ion and Ca-ion batteries, and for improved methods of preparing such salts. The salts and methods described herein address these needs.